1. Field of the Invention
The present invention relates to a projection display with a light-amount control mechanism for adjusting the amount of light applied to a light valve responsive to a video signal.
2. Description of the Background Art
A projection display is apt to have difficulty in ensuring high contrast because dark projected images displayed are not sufficiently dark due to leakage of light from various optical elements in an optical system such as a guide optical system and a projection lens and due to stray light (unnecessary light) caused by the optical elements. In particular for image projection on a screen in a dark room, insufficient darkness of dark projected images on display gives to a viewer the impression of low contrast. Especially in projection displays using liquid crystal light valves, although the liquid crystal light valves block transmitted light in response to the polarization property of light, complete blocking of transmitted light is difficult and there is also a limit in counteractive actions taken by video signal processing so that an improvement in contrast is required.
As a measure to solve this problem, a flat light shielding plate is provided between first and second lens arrays and is turned in response to a video signal to control the amount of light applied to a light valve and thereby to improve the contrast of a projected image on a screen or the like (for example, see WO2005/026835).
In WO2005/026835, in the case where the light shielding plate has at its tip a rectangular plane in a direction vertical to the light shielding plate, if the tip of the light shielding plate is in the vicinity of the first lens array and in a position of the center of the curvature of the second lens array in the turning direction of the light shielding plate, the rectangular plane of the light shielding plate is imaged onto a light valve. This undesirably causes linear unevenness of illumination on the light valve in a direction perpendicular to the turning direction and the optical axis direction. Besides, it is difficult to provide satisfactory contrast depending on the shape of the tip of the light shielding plate.